This invention relates to the preparation of substrates coated by borophosphosilicate glasses, and, more particularly, to a methodology for preparing such coated substrates using chemical vapor deposition.
Borophosphosilicate glass is a dielectric material that is used in microelectronic devices as a separating layer between two electrical conductors. The glass is deposited as a film over an existing layered structure of conductors, semiconductors, and insulators, and further layers are deposited over the glass. The various layers are patterned as required to produce the electronic traces and circuit elements of the microelectronic device. The borophosphosilicate glass can be reflowed (fused) after deposition to change the configuration of the glass film.
One preferred approach to depositing a film of borophosphosilicate glass is by chemical vapor deposition. The various constituents of the glass are provided in properly selected, chemically reactive, gaseous compounds. The compounds are mixed and passed as a gas flow through a reactor and over the substrate upon which the glass is to be deposited. The substrate is heated or otherwise energized. When the gaseous compounds contact the surface of the heated substrate, they react with each other to form a borophosphosilicate glass on the surface.
Some or all of the reactive compounds used to form the gas may be first provided as liquids. Gas vapors of the liquids are produced either by applying heat to vaporize the liquids, or by bubbling a carrier gas through the liquid. The gas vapors are mixed and provided to the reactor.
In one commercial approach to depositing borophosphosilicate glass by chemical vapor deposition, tetraethylorthosilicate (having a formula Si(C.sub.2 H.sub.5 O).sub.4), trimethylborate, and trimethylphosphite gases, mixed with carrier gases, are reacted together at the heated substrate surface to form the glass film. The tetraethylorthosilicate is a relatively toxic, hazardous material. Its handling and disposal present major problems for the user. A large, complex, expensive apparatus is required for gas handling, reaction, control, and disposal. Very tight process controls are required to achieve good-quality films of the glass, and the throughput of product can be slow. Moreover, the films produced by this conventional approach may have marginal electrical properties and conformality.
In an another approach, it has been proposed to deposit the borophosphosilicate glass from a gaseous mixture of tetramethylcyclotetrasiloxane, trimethylborate, trimethylphosphite, and oxygen. This approach has not been commercially successful due to the deposition of impurities onto the substrates and low deposition efficiencies.
There is a need for an improved approach to the production of borophosphosilicate glass films for microelectronic and other applications. The present invention fulfills this need, and further provides related advantages.